This invention relates in general to driveshaft assemblies, such as are commonly used in vehicle drive train systems for transmitting rotational force or torque from an engine/transmission to an axle assembly. In particular, this invention relates to an improved method for manufacturing a driveshaft assembly that is balanced for rotation during use.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. A typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Ideally, the driveshaft tube would be formed in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. Similarly, the end fittings would also be manufactured in such a manner as to be precisely balanced for rotation. Such perfectly shaped end fittings could be secured to the driveshaft tube without affecting the rotational balance characteristics thereof. In actual practice, however, the driveshaft tube and the end fittings usually contain variations in roundness, straightness, wall thickness, and shape that result in minor individual imbalances when rotated at high speeds. As a result, when the end fittings are secured to the driveshaft tube, the combined driveshaft assembly is usually rotationally imbalanced.
To prevent such imbalances from generating undesirable noise or vibration when rotated during use, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft assembly. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft assembly such that it is balanced for rotation during use. Traditionally, the balancing process has been performed through the use of a conventional balancing machine. The balancing machine includes a pair of fittings that are adapted to support the ends of the driveshaft assembly thereon. The balancing machine further includes a motor for rotating the driveshaft assembly at a predetermined speed. As the driveshaft assembly is rotated, the balancing machine senses vibrations that are caused by imbalances in the structure of the driveshaft assembly. The balancing machine is responsive to such vibrations for determining the size and location of one or more balance weights that, if secured to the driveshaft assembly, will minimize these imbalances. The rotation of the driveshaft assembly is then stopped to allow such balance weights to be secured to the driveshaft assembly in a conventional manner, such as by welding, adhesives, and the like. The driveshaft assembly is again rotated to confirm whether proper balance has been achieved or to determine if additional balance weights are required.
Although this method has been effective, this balancing process has been found to be relatively slow and inefficient. This is because each driveshaft tube must usually be rotated and measured at least two times, a first time to measure the imbalances and determine the size and location of the balance weights, and a second time to confirm that proper balance has been achieved after the balance weights have been secured thereto. This time consuming process is particularly problematic in the context of balancing vehicular driveshaft tubes, which are typically manufactured in relatively large volumes. Thus, it would be desirable to provide an improved apparatus and method for quickly and efficiently balancing an article, such a tube for use in a vehicular driveshaft assembly, for rotation about an axis.
Conventional end fittings are typically formed by a forging process. In the forging process, a slug of raw material, usually aluminum, is inserted into the cavity of a die. The cavity defines the general shape of the end fitting. A punch applies a compressive force against the slug to cause the slug to assume the shape of the cavity. As a result of the forging process, an asymmetrical raw part is formed. The raw part is machined to form the end fitting. The end fittings are welded to each end of the driveshaft tube to form the driveshaft assembly. After manufacture, the driveshaft assembly must be precisely balanced for rotation to prevent undesirable noise and vibration. This is typically accomplished by determining the amount and location of imbalance of the driveshaft assembly and securing an appropriate counter weight to the driveshaft assembly to offset such imbalance. By convention, the manufacturing and the balancing of the driveshaft assembly have been performed as two separate and unrelated operations. That is to say, the driveshaft assembly has been completely manufactured and then balanced. This can result in a driveshaft assembly that is greatly imbalanced if the heavy side of one or both of the end fittings is aligned with the heavy side of the driveshaft tube.
This invention relates to an improved method for manufacturing a driveshaft assembly that takes advantage of the asymmetrical nature of the driveshaft tube and the end fittings to reduce the imbalance of the driveshaft assembly. The method comprises the initial steps of providing a driveshaft tube having a heavy side and providing an end fitting having a heavy side. The heavy side of the end fitting is aligned so as to be opposite the heavy side of the driveshaft tube. Finally, the driveshaft tube and the end fitting are secured together. The dimensional characteristics of the driveshaft tube and end fitting improve the balancing capability of the driveshaft assembly by permitting levels of imbalance of the driveshaft assembly to be lowered and better-managed.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.